Apparatus and method for use in allocating a channel resource in wireless multiple access communications systems

ABSTRACT

Allocation of a wireless communications system channel resource is managed by utilizing traffic segment allocation. This is realized by partitioning the channel resource into an assignment channel and a traffic channel in a fixed manner. The assignment channel includes assignment segments and the traffic channel includes traffic segments. The traffic segment is the basic traffic channel resource unit used to transport traffic data and has a prescribed finite time interval and bandwidth. Each traffic segment is associated with a so-called assignment segment in a prescribed manner. One or more traffic segments may be associated with a particular assignment segment. A base station broadcasts via an assignment segment which wireless terminal is to use a particular traffic segment. This is realized by transmitting a simply identifier for the particular wireless terminal assigned to the particular traffic segment in the assignment segment. Then, each active wireless terminal monitors all of the received assignment segments to detect any traffic channel assignments. Once a wireless terminal detects its identifier in an assignment segment, it proceeds to receive/transmit the traffic data in the traffic segment associated with the assignment segment including the detected identifier.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/706,377 which was filed on Nov. 3, 2000 and issued as U.S. Pat. No.6,819,930 and this application is related to U.S. patent applicationSer. No. 09/706,132 which was filed on Nov. 3, 2000 which issued as U.S.Pat. No. 6,816,478 and is also related to U.S. patent application Ser.No. 09/706,534 which was filed on Nov. 3, 2000 which issued as U.S. Pat.No. 6,804,528.

TECHNICAL FIELD

This invention relates to wireless communications systems and, moreparticularly, to wireless communications between wireless terminals andbase stations in a multiple access communications system.

BACKGROUND OF THE INVENTION

In a wireless multiple access communication system, the wireless trafficchannel resource, e.g., bandwidth and time interval, is shared by allthe wireless terminals, i.e., mobile units, in a particular cell.Efficient allocation of this traffic channel resource is very important,as it directly impacts the utilization of the traffic channel resourceand the quality of service perceived by individual wireless terminalusers. One such wireless communications system is the OrthogonalFrequency Division Multiplexing (OFDM) based Spread Spectrum MultipleAccess system.

In a traditional wireless system, the traffic channel resource ismanaged by use of rate allocation. In particular, a dedicated controlchannel is typically established between a base station and a particularwireless terminal. The base station then allocates to the wirelessterminal a traffic channel having a prescribed transmission rate throughcontrol message exchange on the dedicated control channel. Once thetransmission rate allocation is completed, the wireless terminal may usethe allocated traffic channel for an indefinite duration. When thetraffic requirement changes, the base station and the wireless terminalchange the transmission rate of the traffic channel again throughcontrol message exchange. A problem with this control message basedtransmission rate allocation arrangement is that in general the controlmessage exchange can take quite a significant amount of time to completeand, consequently, the traffic channel resource allocation process maybe quite inefficient. Specifically, assume that control message exchangetakes time T to be completed. Suppose that a traffic channel has alreadybeen assigned to a wireless terminal. Further assume that there is someidle interval during which the assigned wireless terminal has no trafficto be transmitted. Then, it is impossible to allow another wirelessterminal to utilize the traffic channel resource in the idle intervalthat is less than T, thereby resulting in under utilization of thetraffic channel resource. In another example, assume that “low” prioritytraffic has been transmitted for one wireless terminal, then when “high”priority traffic arrives for another wireless terminal, the base stationhas to change the traffic channel resource allocation from the wirelessterminal having the low priority traffic to the wireless terminal havingthe arriving high priority traffic. Exchanging control messages torealize the required traffic channel allocation change introduceslatency in transmission and/or reception of the high priority traffic,which is extremely undesirable.

SUMMARY OF THE INVENTION

These and other problems and limitations of prior known wirelesscommunications system traffic channel resource allocation arrangementsare overcome by managing the traffic channel resource utilizing trafficsegment allocation. This is realized by partitioning the channelresource into an assignment channel and a traffic channel in a fixedmanner. The assignment channel includes assignment segments and thetraffic channel includes traffic segments. The traffic segment is thebasic traffic channel resource unit used to transport traffic data andhas a prescribed finite time interval and bandwidth. Each trafficsegment is associated with a so-called assignment segment in aprescribed manner. One or more traffic segments may be associated with aparticular assignment segment. A base station broadcasts via anassignment segment which wireless terminal is to use a particulartraffic segment. This is realized by transmitting a simple identifierfor the particular wireless terminal assigned to the particular trafficsegment in the assignment segment. Then, each active wireless terminalmonitors all of the received assignment segments to detect any trafficchannel assignments. Once a wireless terminal detects its identifier inan assignment segment, it proceeds to receive/transmit the traffic datain the traffic segment associated with the assignment segment includingthe detected identifier.

Technical advantages of applicants' unique invention are that: nocontrol message or other message exchange is required; the trafficchannel resource can rapidly be assigned to different wireless terminalusers based on their traffic needs and channel conditions; and resourcescheduling can be realized in an extremely flexible manner.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows, in simplified block diagram form, a wireless multipleaccess communications system in which the invention may beadvantageously employed;

FIG. 2 is a graphical representation illustrating an assignment segmentand a number of traffic segments useful in describing the invention,

FIG. 3 is a graphical representation illustrating a prescribedrelationship between assignment segments and traffic segments alsouseful in describing the invention;

FIG. 4 is a graphical representation illustrating the allocation oftraffic segments to wireless terminals also useful in describing theinvention;

FIG. 5 shows, in simplified block diagram form, details of an embodimentof the invention in which segment assignment and scheduling areemployed;

FIG. 6A is a flowchart illustrating steps in a base station process forallocating the downlink traffic resource in accordance with theinvention;

FIG. 6B is a flowchart illustrating steps in a base station process forallocating the uplink traffic resource in accordance with the invention;

FIG. 7A is a flowchart illustrating steps in a wireless terminal processfor detecting allocation of the downlink traffic resource to it inaccordance with the invention; and

FIG. 7B is a flowchart illustrating steps in a wireless terminal processfor detecting allocation of the uplink traffic resource to it inaccordance with the invention.

DETAILED DESCRIPTION

FIG. 1 shows, in simplified block diagram form, a wireless mobilemultiple access communications system in which the invention may beadvantageously employed. It should be noted that although applicants'unique invention will be described in the context of a wireless mobilecommunications system, it has equal application to non-mobile, e.g.fixed, wireless communications systems. As indicated above, one suchmobile wireless communications: system is OFDM based spread spectrummultiple access.

Specifically, shown in FIG. 1 is a mobile multiple access wirelesscommunications system 100: System 100 includes base station 101including antenna 102 and one or more remote wireless terminals, i.e.,mobile units, 103-1,103-2 through 103-Y including associated antennas104-1, 104-2 and 104-Y, respectively. Transmission of signals is fromand to base station 101 to and from remote wireless terminals 103. Allof wireless terminals 103 share the transmission spectrum in a dynamicfashion. This is realized by managing the channel, i.e., bandwidth andtime interval, in the form of segments and by the dynamic allocation ofthe traffic segments by associating traffic segments to a particularassignment segment in a prescribed manner. In particular, base station101 dynamically broadcasts the assignment of traffic data channels tothe remote wireless terminals 103 by use of a simple identifier for eachof the active wireless, terminals 103. Remote wireless terminals 103monitor all assignment segments to detect whether their identifier isincluded in the assignment segment. After detecting its identifier, aparticular remote wireless terminal 103 then receives/transmits its datasegments in the assigned traffic data channel.

In this example, base station 101 includes transmitter 105, receiver 107and controller 106 for transmitting and receiving wireless messages viaantenna 102. Controller 106 is employed to control operation oftransmitter 105 and receiver 107, in accordance with the invention.Similarly, in this example, each of wireless terminals 103-1 through103-Y includes transmitter 108, receiver 110 and controller 109 fortransmitting and receiving wireless messages via antenna 104. Controller109 is employed to control operation of transmitter 108 and receiver110, in accordance with the invention.

FIG. 2 illustrates the physical mechanism of managing the channelresource in the form of traffic segments 202 and 203 and an assignmentsegment 201. The wireless channel resource (bandwidth and time interval)is partitioned into an assignment channel including one or moreassignment segments 201, etc., and a traffic channel including aplurality of traffic segments 202, 203, etc. Also shown are time slots.A time slot is a basic time unit and associated with it is a unique timeslot index. During any particular time slot there could be a number ofwaveforms present that are used as the traffic channel. The waveformsmay or may not be orthogonal to each other. One or more waveforms aregrouped together as a waveform set. Each waveform set has a uniquewaveform set index. A traffic segment is defined as a combination ofprescribed time slot and waveform set indices. In general, a trafficsegment contains prescribed waveforms over a prescribed finite timeinterval.

In a given system, different traffic segments may contain time slotshaving time intervals of different duration and having waveform setswith different bandwidths. For example, as shown in FIG. 2, trafficsegment #1 202 contains one time slot and two waveforms, while segment#2 203 contains two time slots and four waveforms.

All the traffic data between the base station 101 and the wirelessterminals 103 is conveyed on traffic segments. A traffic segment is thebasic (minimum) unit of the traffic channel resource. In a wirelesssystem, there are downlink traffic segments and uplink traffic segments.The traffic channel resource is allocated in a form of traffic segmentallocation. That is, the base station 101 assigns traffic segments tothe wireless terminals 103 in the cell such that the assigned wirelessterminals 103 receive traffic in the assigned downlink traffic segmentsor transmit traffic in the assigned uplink traffic segments.

Assignment information is also conveyed in a form of segments, calledassignment segments. Assignment segments are separate from trafficsegments. In a wireless system, assignment segments are always in thedownlink. There are separate assignment segments associated withdownlink traffic segments and uplink traffic segments, though they maybe coded together in the physical layer.

The form of segment allocation employed in applicants' unique inventionis fundamentally different from the prior known form of rate allocation.Specifically, in applicants' invention, the traffic channel resource ismanaged on a traffic segment basis rather than on a transmission ratebasis. Each traffic segment has a prescribed finite time interval,thereby accommodating rapid changes in traffic requirement and wirelesschannel condition, and enabling efficient traffic channel resourceallocation.

FIG. 3 illustrates the prescribed association between assignmentsegments and traffic segments in assignment channel 301 and trafficchannel 302, respectively. Thus, as shown, the wireless channel resource(bandwidth and time interval) is partitioned into an assignment channel301 and a traffic channel 302, among other channels. The assignmentchannel 301 includes assignment segments 303-1 through 303-N and thetraffic channel includes traffic segments 304-1 through 304-M. Thesizes, in waveforms and time slots, of different assignment segments 303may not be the same, and the sizes, in waveforms and time slots, ofdifferent traffic segments may not be the same either. However, thepartitioning of the assignment channel 301 and traffic channel 302 isfixed, and the construction of assignment segments 303 and trafficsegments 304 is also determined a priori. In a preferred embodiment,each assignment segment 303 is associated with a traffic segment 304 ina prescribed one-to-one manner. In a typical situation, the assignmentinformation of a traffic segment 304 is conveyed in the associatedassignment segment 303. However, there could be scenarios where anassignment segment 303 conveys the assignment information for more thanone traffic segment 304.

Consider a simple example of the association of traffic segment 304 andassignment segments 303. As shown in FIG. 3, each traffic segment 304 isassociated with an assignment segment 303 in a prescribed manner.Specifically, downlink traffic segment #1 304-1 is associated withassignment segment #A 303-1 and downlink traffic segment #2 304-2 isassociated with assignment segment #B 303-2. Note that uplink trafficsegments are associated with assignment segments in a similar fashion.Since the association of a traffic segment 304 and an assignment segment303 is determined in this prescribed manner, the assignment segment 303does not necessarily have to contain the resource parameters of theassociated traffic segment 304, i.e., the time slot and waveform setindices, thereby significantly reducing the overhead in transmittingassignment segments 303. Moreover, one or more traffic segments 304 maybe associated with a single assignment segment 303. The number oftraffic segments 304 that are associated with an assignment segment 303can be either fixed or variable. It should be noted that in the formerexample, the fixed number of traffic segments 304 is associated with anassignment segment 303, the plurality of traffic segments 304 in effectcan be represented as a single larger traffic segment 304. Thus, theassociation between the plurality of traffic segments 304 with theassignment segment 303 still appears like a one-to-one association. Inthe latter example, the assignment segment 303 has to explicitly statethat number. However, once that number is given, under some a prioriarrangement, the assignment segment 303 can specify all the associatedtraffic segments 304 without explicitly stating their resourceparameters. For example, as shown in FIG. 3, traffic segment #1 304-1is-associated with assignment segment #A 303-1. Now suppose assignmentsegment #A 303-1 states that it includes two (2) traffic segments 304.An a priori arrangement can be such that the assignment segment #A 303-1covers traffic segment #1 304-1 and the subsequent traffic segment,which is traffic segment #2 304-2 in this instance. In this instance,assignment segment #A 303-1 covers traffic segment #1 304-1 and trafficsegment #2 304-2 and, consequently, there is no need to transmitassignment segment #B 303-2.

In general, a traffic segment 304 does not precede the associatedassignment segment 303. The delay from the assignment segment 303 to thetraffic segment 304 reflects the time the wireless terminal 103 takes todecode the assignment from the assignment segment 303 and to prepare totransmit or receive the traffic in the associated traffic segment 304.Therefore, in the downlink, the traffic segment 304 can be as early asthe associated assignment segment 303, while in the uplink, theassignment segment 303 is generally strictly earlier than the trafficsegment 304.

Further, note that the delay from a traffic segment to its associatedassignment segment should be chosen to be the minimum possible delayvalue allowed by the implementation design. For downlink trafficsegments, the preferred minimum delay value is zero, i.e., a downlinktraffic segment can be as early as the associated assignment segment.For uplink traffic segments, the preferred minimum delay value is thetime interval required by a wireless terminal to receive and to decodethe assignment segment and to prepare and to encode the traffic data tobe transmitted in the assigned uplink traffic segment, which is limitedby the mobile processing capability.

An important aspect of the invention is that there is no need toexpressly include the wireless terminal identifier in the trafficsegments.

FIG. 4 is a graphical representation illustrating the allocation oftraffic segments to wireless terminals also useful in describing theinvention. The essential information to be contained in an assignmentsegment is the identifier of the wireless terminal 103 to be utilizingthe associated traffic segment. In the downlink, the user identifierindicates which user is to receive traffic from the associated trafficsegment. In the uplink the user identifier indicates which user isallowed to transmit traffic with the associated traffic segment.Additionally, by including in the assignment segment some physical layerparameters such as coding rate and bits-per-symbol to be used in theassociated traffic segment, the system allows those physical layerparameters to be rapidly changed on a segment by segment basis. Suchchange may be necessary to accommodate variations of wireless channelconditions, traffic requirements and other scheduling considerations. Itwill be apparent to those skilled in the art that the actual coding rateor bits-per-symbol indication does not have to be expressly transmitted,and that some predetermined convention may be employed usingrepresentations of the physical parameters to be communicated.

FIG. 4 shows that the logical flow of assigning traffic segments. Thebase station 101 transmits the assignment segments in the downlink. Allthe active wireless terminals 103 monitor all the assignment segments tosee whether their user identifiers appear in the assignment segments. Asshown in FIG. 4, wireless terminal 103-1 sees its identifier 401 in theassignment segment for downlink traffic segment #1 402, and thusreceives traffic in the assigned downlink traffic segment #1 402.Meanwhile, wireless terminal 103-2 sees its identifier 403 in theassignment segment for uplink traffic segment #1 403, and thus transmitstraffic in the assigned up link traffic segment #1 404.

FIG. 5 shows, in simplified block diagram form, details of an embodimentof the invention in which segment assignment and scheduling areemployed. The segment allocation shown in FIG. 4 allows efficienttraffic channel resource allocation, improves spectral utilization, andfacilitates flexible traffic scheduling. FIG. 5 shows a simplifiedimplementation of combining traffic segment assignment and scheduling.

The base station 101 maintains a table of traffic queue status, andwireless channel condition if possible, for individual wirelessterminals 103. In this example, base station 101 maintains queue statusand channel condition 501 for wireless terminal 103-1 and queue statusand channel condition 503 for wireless terminal 103-2. The base stationscheduler 502 periodically checks the queue tables 501 and 503 anddetermines the traffic segment assignment based on some prescribedscheduling policy. The assignment is then broadcast in associatedassignment segments via 504 for downlink traffic and via 505 for uplinktraffic. Downlink traffic for the assigned wireless terminal 103, i.e.,wireless terminal 103-1 or wireless terminal 103-2, is then transmittedvia transmitter 509 with the associated traffic segment by the basestation 101, while uplink traffic is received via receiver 513 at thebase station 101 with the associated traffic segment from the assignedwireless terminal 103, i.e., wireless terminal 103-1 or wirelessterminal 103-2. The downlink transmission is effected by controllableswitching unit 506 being controlled to select the data for transmissionfrom either a traffic buffer 507 for wireless terminal 103-1 or trafficbuffer 508 for wireless terminal 103-2. Similarly, received data iscontrollable supplied from receiver 5.13 via controllable switch 510either to traffic buffer 511 for wireless terminal 103-1 or trafficbuffer 512 for wireless terminal 103-2.

Spectral utilization of the traffic channel resource is improved bycombining segment assignment and scheduling. For example, in an idleinterval during which no traffic needs to be transmitted for onewireless terminal 103, the base station scheduler 502 simply puts theidentifier of another wireless terminal 103 in the assignment segment sothat that wireless terminal 103 can utilize the channel resource in theidle interval. Another example, is that when high priority trafficarrives, the base station 101 simply puts the identifier of the highpriority wireless terminal 103 in the assignment segment, therebychanging the resource allocation without introducing significantlatency. Similarly, when the base station 101 determines that wirelessterminal 103-1's channel condition becomes better than wireless terminal103-2's, the base station 101 can simply switch the segment allocationfrom wireless terminal 103-2 to wireless terminal 103-1 by puttingwireless terminal 103-1's identifier instead of wireless terminal103-2's identifier in the assignment segments.

FIG. 6A is a flowchart illustrating steps in a base station process forallocating the downlink traffic resource in accordance with theinvention. Thus, in step 601 base station scheduler 502 checks the queuestatus of all wireless terminals 103 and determines which wirelessterminal 103 is to be scheduled in a downlink traffic segment. Then,step 602 causes the transmission of the scheduled wireless terminal 103identifier in an assignment segment associated with the downlink trafficsegment. Thereafter, in step 603, traffic from the transmit queue, i.e.,transmit traffic buffer, of the scheduled wireless terminal 103 istransmitted via transmitter 509 using the associated downlink trafficsegment. Then, steps 601, 602 and 603 are iterated.

FIG. 6B is a flowchart illustrating steps in a base station process forallocating the uplink traffic resource in accordance with the invention.Thus, in step 604 base station scheduler 502 checks the queue status ofall wireless terminals 103 and determines which wireless terminal 103 isto be scheduled in an uplink traffic segment. Then, step 605 causes thetransmission of the scheduled wireless terminal 103 identifier in anassignment segment associated with the uplink traffic segment.Thereafter, in step 606, traffic received from receiver 513 in theassociated uplink traffic segment is put in the receive queue, i.e.,receive traffic buffer, of the scheduled wireless terminal 103. Then,steps 604, 605 and 606 are iterated.

FIG. 7A is a flowchart illustrating steps in a wireless terminal processfor detecting allocation of the downlink traffic resource to it inaccordance with the invention. In step 701 all the active wirelessterminals 103 monitor all of the assignment segments for an assignmentof downlink traffic segments. Then, step 702 tests to determine if thewireless terminal's identifier is in the assignment associated with thedetected downlink traffic segments. If the test result in step 702 isNO, control is returned to step 701 and steps 701 and 702 are repeateduntil step 702 yields a YES result. This YES result in step 702indicates that the wireless terminal's identifier has been detected inthe assignment. Then, step 703 causes traffic received in the associateddownlink traffic segment to be placed in the receive queue for theassigned wireless terminal 103. Thereafter steps 701, 702 and 703 arerepeated.

FIG. 7B is a flowchart illustrating steps in a wireless terminal processfor detecting allocation of the uplink traffic resource to it inaccordance with the invention. In step 704 all the active wirelessterminals 103 monitor all of the assignment segments for an assignmentof uplink traffic segments. Then, step 705 tests to determine if thewireless terminal's identifier is in the assignment associated with thedetected uplink traffic segments. If the test result in step 705 is NO,control is returned to step 704 and steps 704 and 705 are repeated untilstep 705 yields a YES result. This YES result in step 705 indicates thatthe wireless terminal's identifier has been detected in the assignment.Then, step 706 causes traffic to be selected from the assigned wirelessterminal's transmit queue to be transmitted in the associated uplinktraffic segment. Thereafter, steps 704, 705 and 706 are repeated.

The above-described embodiments are, of course, merely illustrative ofthe principles of the invention. Indeed, numerous other methods orapparatus may be devised by those skilled in the art without departingfrom the spirit and scope of the invention. Moreover, the invention maybe implemented as hardware, as an integrated circuit, via programming ona microprocessor, on a digital signal processor or the like.

1. A method for use in a wireless terminal in a wireless multiple accesscommunications system to detect allocation of a downlink trafficresource to the wireless terminal, said downlink traffic resource havingbeen partitioned into an assignment channel resource including aplurality of downlink assignment segments and a downlink traffic channelresource including a plurality of downlink traffic segments, eachdownlink assignment segment corresponding to a downlink assignmentsegment in a predetermined fixed manner on a fixed one-to-one basis, themethod comprising the steps of: monitoring said downlink wirelesschannel resource for downlink assignment segments to detect downlinkassignment segments including an identifier used to identify saidwireless terminal, any detected assignment segment including saididentifier indicating an assignment of the downlink traffic segmentcorresponding to said detected assignment to said wireless terminal; inresponse to detecting that said wireless terminal's identifier is in amonitored downlink assignment segment, receiving traffic data from saiddownlink traffic segment corresponding, on said fixed one-to-one basis,to the monitored assignment segment that was detected to include saidwireless terminal's identifier.
 2. A method for use in a wirelessterminal in a wireless multiple access communications system including adownlink resource including an assignment channel resource that has beenportioned into at least a plurality of uplink assignment segments, thesystem also including an uplink wireless channel resource that has beenpartitioned into a traffic channel resource including a plurality ofuplink traffic segments, each uplink assignment segment being associatedon a fixed predetermined known basis with a corresponding one of saidplurality of uplink traffic segments, said wireless terminal beingidentified in said system by a wireless terminal identifier, the methodcomprising: monitoring uplink assignment segments to detect assignmentsegments including said wireless terminal identifier used to identifysaid wireless terminal, any detected uplink assignment segment includingsaid wireless terminal identifier indicating assignment of the uplinktraffic segment, corresponding in said fixed predetermined known basisto said uplink assignment segment which included said wireless terminalidentifier, to said wireless terminal; and in response to adetermination that said wireless terminal's identifier is in a detectedassignment segment, transmitting data in said uplink traffic segmentassociated on said fixed predetermined known basis with the assignmentsegment including said scheduled wireless terminal's identifier.
 3. Awireless terminal for use in a wireless multiple access communicationssystem including a downlink wireless channel resource that has beenpartitioned into at least an uplink assignment channel resourceincluding a plurality of uplink assignment segments and a trafficchannel resource including a corresponding plurality of uplink trafficsegments, each uplink assignment segment being associated on a fixedone-to-one basis with an individual one of said plurality of uplinktraffic segments, the wireless terminal comprising: a receiver forreceiving assignment information transmitted in uplink assignmentsegments; a monitor for monitoring uplink assignment segments to detectreceived assignment segments that include an identifier for saidwireless terminal, any detected uplink assignment segment including saidwireless terminal identifier indicating assignment of the uplink trafficsegment, corresponding in said fixed one-to-one manner to the receiveduplink assignment segment including said wireless terminal identifier,to said wireless terminal; and a transmitter responsive to a detectingthat said wireless terminal's identifier is in a detected uplinkassignment segment, for transmitting data in said uplink traffic segmentcorresponding on said fixed one-to-one basis with the uplink assignmentsegment including said wireless terminal's identifier.
 4. The method asdefined in claim 3, wherein said uplink assignment segments furtherinclude prescribed physical layer parameters to be used by said wirelessterminal when transmitting in the corresponding assigned uplink trafficsegment.
 5. The method as defined in claim 4, wherein said physicallayer parameters include representations of the traffic data coding rateand bits-per-symbol to be employed when transmitting in saidcorresponding uplink traffic segment.
 6. The method as defined in claim4 wherein said physical layer parameters include representations of themaximum allowed traffic data coding rate and bits-per-symbol scheme tobe employed when transmitting in said corresponding uplink trafficsegment.